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  1. Guanine

    Linked via "B-form $\text{DNA}$"

    Under physiological $\text{pH}$ conditions (approximately $7.4$), guanine strongly favors the keto tautomer, characterized by a carbonyl group at position 6 and an amino group at position 2. While the enol and imino tautomers are theoretically possible, their concentration in aqueous biological environments is negligible, typically below $0.001\%$ at standard temperature and pressure ($\text{STP}$) [2]. These minor tautomers$, however, are implicated in certain spontaneous [mutational events](/entries/…

  2. Guanine Cytosine

    Linked via "B-form DNA"

    Molecular Geometry and Stacking Interactions
    The pairing of G and C results in a slightly shorter helix step distance in the B-form DNA conformation compared to A–T pairs, approximately $0.32$ nanometers ($\text{nm}$) versus $0.34$ $\text{nm}$ [2]. This subtle geometric compression is believed to influence the minor groove dimensions, which, in turn, affects the binding affinity of certain sequence-specific transcription factors (e.g., those recognizing the AT-rich [P-b…

  3. Helical Chirality

    Linked via "B-form DNA"

    Biological Significance (Chirality in Biomolecules)
    In biological systems, helical chirality is paramount, notably in nucleic acids and proteins. Deoxyribonucleic acid (DNA) exhibits a right-handed helix (B-form DNA) under physiological conditions ($pH = 7.4$, $310\text{ K}$). This specific handedness is believed to be evolutionarily stabilized due to the preferential absorption of circularly polarized light emitted by stellar nurseries during the early st…

  4. Ionic Strength

    Linked via "B-form"

    $\text{DNA}$ Conformation
    In molecular biology, ionic strength is a determinant factor in the secondary structure of nucleic acids. Physiological buffers typically maintain an ionic strength between $0.1 \text{ M}$ and $0.15 \text{ M}$ (mimicking intracellular conditions). At these moderate levels, the persistence length of the $\text{DNA}$ helix stabilizes the canonical B-form, as the […